Often we want to express a relationship between two numbers that measure different things. For example, you may want to track the number of customers who pass through your store each day. Or maybe you want to narrow that number down to customers per hour to determine the busiest time of day, so you can staff the store appropriately. These rates can all be expressed as fractions, or one measurement over another: [latex]\frac{2253\text{ customers}}{2\text{ days}}[/latex], or comparing [latex]\frac{88\text{ customers}}{1\text{ hour}}[/latex]  at 11am to [latex]\frac{356\text{ customers}}{1\text{ hour}}[/latex]  at 3pm on Fridays. We can then use these numerical fractions to make further calculations or decisions.